BASIS OF PRESENTATION AND ACCOUNTING POLICIES - Narrative (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) branch	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of branches operated | branch	125
Reserve requirement	$ 58,200		$ 44,100
Stranded tax effects			$ 392
Reclassification to retained earnings due to change in federal corporate tax rate	(392)
Accumulated Other Comprehensive Income (Loss), Net of Tax
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification to retained earnings due to change in federal corporate tax rate	(392)	$ 0
Accumulated Other Comprehensive Income (Loss), Net of Tax | Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification to retained earnings due to change in federal corporate tax rate	(392)
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification to retained earnings due to change in federal corporate tax rate	392	$ 0
Retained Earnings | Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification to retained earnings due to change in federal corporate tax rate	$ 392
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Acquired finite-lived intangible assets, weighted average useful life	7 years
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Acquired finite-lived intangible assets, weighted average useful life	10 years
US Premium Financing Holding Company | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Acquired finite-lived intangible assets, weighted average useful life	3 years
US Premium Financing Holding Company | Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Acquired finite-lived intangible assets, weighted average useful life	8 years